When a plurality of inkjet nozzles is connected to a pressurized ink cavity, it is desirable that the droplets produced from the stream passing through each of the nozzles have substantially the same breakoff point, be substantially uniform in size, have substantially uniform space between the droplets, and be satellite free. This insures that the quality of the print from each of the nozzles will be substantially the same.
To obtain this uniformity between the droplets of the various streams, it is necessary that the perturbations applied to each ink stream be substantially uniform, and that the nozzle be of uniform quality. Furthermore, for the production of the droplets to be satellite free, it is also necessary that the perturbations be sufficiently strong. It is also necessary for the perturbations not only to be substantially uniform, but to be reproducible throughout the time the droplets are being produced.
To meet these basic requirements, it is necessary that the transducer or driver producing the vibrations for causing perturbations in the ink streams be capable of operation so that the amplitude of each of the pressure waves produced in the ink cavity by the driver is substantially the same at the entrance to each inkjet nozzle. This will produce uniform perturbations in the inkjet streams flowing through the nozzles. It is also necessary for the amplitude of the pressure waves to be sufficiently high to produce satellite free droplets
With respect to the intended orientation of the various components in the total structure, it should be understood that the length of both the transducer and the ink cavity is parallel to a line connecting the entrances of the nozzles of the array. Thus, the required transducer vibration mode that produces uniform perturbations for the array of inkjet stream is that in which the vibrations are "in phase" along the length direction of the transducers, and that the amplitudes are uniform for a sufficient portion of the transducer length along which the nozzle array is in alignment. This vibration mode is typically referred to as a symmetrical mode of operation.
While the foregoing describes what is necessary to produce uniform perturbations for the array of inkjet streams, non-uniformity of the perturbations in the ink streams is due both to non-symmetrical driver vibrations and end conditions. Non-symmetrical driver vibrations are those which are not in phase along the length direction and/or non-uniform in amplitude.
One cause of end conditions is due to the end walls of the ink cavity acting on the ink as the pressure wave moves through the ink in the ink cavity. This diminishes the amplitude of the pressure wave.
Another source of irregular output is the presence of bubbles in the ink stream. These occur especially in large size ink cavities such as are typical of prior art systems.